Film driving means



Feb. 15, 1938. l.. B. HOFFMANN FILM DRIVING MEANS Filed N OV. 2, 1956 5 Sheets-Sheet l lnvenlon 's B. Hoffmann.

y l'l'orney.

Fel. 15, 193s. L a HOFFMANN 2,108,337

FILM DRIVING MEANS Filed Nov. 2, 1936 3 Sheets-Sheet 2 Invenlor. Louis Half/mann Patented Feb. 15, 1938 LnouisI lB.

offmann, Hollywood, Calif., assignor to Mitc ell Camera Corporation, West Hollywood, Calif., a corporation of Delaware Application November z, 193s, serial No. 108,780y

8 Claims.

'This invention relates generally to sound' picture recording and reproducing apparatus, and more particularly to means for driving a film at constant/speed for sound wave translation in 5 sound picture lrecording or projection apparatus.

As is well known, it is essential in recording or reproducing sound on or from a sound film that the film may be moved past the recording or reproducing light beam with a high degree of l steadlness or uniformity of motion, as-slight variations or fluctuations in sound record speed are reflected in the reproduced sound either as very noticeable and highly objectionable pitch variations, as a higher frequency flutter, or as simple roughness, depending upon the frequency of the speed fluctuations that occur.

It is a primary object of the present invention to provide improved means for moving the sound record nlm past the sound wave translation point with a high degree of uniformity of speed, both in recording and reproduction of sound.

While the present invention is applicable either to recording or reproduction of sound, it is particularly applicable and useful in its adaptation to recording apparatus, and will therefore be re ferred to particularly in that connection, though without necessary implied limitation to such use.

In accordance with the present invention, the film strip coming from the feed reel engages first one side of a driven sprocket, from there passes over a yieldingly mounted tensioning roller, and then goes to a smooth faced rotatable drum which is provided with an inertia mass suflicient to insure steadiness of motion. Leaving this drum, which is driven by the moving film strip, the film passes over a second yieldingly mounted tensioning roller and then goes to a driving sprocket which is driven through a mechanical filter from the same source of power that drives'the first mentioned sprocket. This second sprocket is also provided with an inertia mass, so that speed fluctuations in the drive mechanism are absorbed in the mechanical filter and are not transmitted to the sprocket. From 4.-, this second sprocket the film goes to the other side of the first mentioned sprocket, and from there is taken to the take-up reel. The first sprocket thus acts as a drivenahold-back member,

and the second sprocket, which is driven with .'.o substantially perfect uniformity of motion owing to the filter and fly wheel, pulls the film around the smooth faced inertia mass drum, causing said drum to rotate. The two yieldlngly mounted tensioning rollers between the two sprockets and 5,-, the drum maintain aconstant tension on the film, and the roller between the first sprocket and the drum prevents speed fluctuations of said sprocket from being transmitted to the drum.

The second sprocket being steadied by the fly Wheel and filter combination, is not subject to speed fluctuations, but any jerkiness arising from sprocket tooth action is absorbedby the second tensioning roller.

Various additional objects and features of the invention will appear in the following detailed description of a present preferred embodiment thereof, reference for this purpose being had to the accompanying drawings, in which:

Fig. 1 is a view showing a sound recording unit in accordance with the present invention;

Fig. 2 is a vertical sectiontaken on line 2-2 of Fig. 1;

Fig. 3 is a vertical section taken on line 3-3 of Fig. 1;

Fig. 4 is a vertical section taken on line 4--4 of Fig. 3, the housing wall being omitted;

Fig. 5 is a verticalsection taken on line 5-5 of Fig. 3, the housing wall being omitted;

Fig. 6 is a vertical section taken on line 6--6 of Fig. 1; and

Fig. 7 is a horizontal section taken on line 1--1 of Fig. 1.

The recording apparatus is generally indicated in the drawings at I0, and is shown provided with a casing II supporting magazine I2 containing the feed and take-up film rolls I3 and I4. respectively. The film and take-up rolls are mounted on reels, not shown, the take-up reel being providedwith any suitable or well known take-up drive means, not necessary here to illustrate.

lThe film strip F coming from fed roll I3 passes downwardly from magazine I2 over idler roller I8, entering recorder case I I through aperture I1 and passing downwardly to engage one side of a film sprocket 20. The film strip eventually engages the opposite side of this same sprocket 20 and then passes upwardly through aperture I1 to take-up reel I4. The film is held in engagement with sprocket 20 by retaining rolls 2I of any conventional type.

As shown best in Fig. 2, sprocket 20 is rigidly mounted on the outer end of a shaft 24 which is journalled in bearings 25 carried by a tubular boss 25a on a plate 26 mounted on casing wall 21. The opposite end of shaft24 is journalled in a bearing 29 carried by a gear housing 30 formed integrally with wall .21, and non-rotatably mounted on shaft 24 within said housing 30 is a worm wheel 32 driven by a worm 33 on a horizontal main drive shaft 34 extending through housing l Gil 8l and journalled at its ends in suitable bearings at 88 and 88 supported in any suitable manner by the sides of the exterior easing (see rig. 7).

Shaft 24 is here illustrated as also carrying a belt pulley 88, which may be understood u driving a belt which operates the take-up reel. Since the driving connection between pulley 38 and the take-up reel forms no part of the present invention, no showing thereof is made in the drawings.

Shaft 84 has a portion Maextending outside the casing, and mounted thereon is a coupling member 88 connected through flexible ring 41 to a coupling member 48 on a drive shaft 48, which will be understood to be driven by any suitable motor not shown.

From film sprocket 28, the film strip passes over a tensioning roller 40 and then goes to a smooth vfilm drum 4|, preferably of comparatively large diameter, as substantially six inches in diameter. This drum 4| is non-rotatably mounted on a shaft 42 journalled in bearings 43 Supported by wall 21. This drum 4| is lmounted below sprocket 28. and its laxis is somewhat ofi-set to the right from the axis of `drum 28, as seenvin Fig. 1. Ithas been stated that drum 4| is a smooth surfaced film drum; by this is meant that the drum is not provided with sprocket teeth. The peripheral `lm engaging surface 41a of .the drum is, however,vrecessed at 45 and 48 directly opposite the perforations of the film strip passing over it. This is of advantage in that, any roughv or bent edges of the perforations are thereby prevented from engaging the drum and influencing its steadiness of rotation. Recess 46 is preferably of thel combined width of the perforations and sound track, and is painted black to reduce renection of light.

Inside of bearing 48 shaft 42 is provided with an inertia mass or y wheel 50, here shown as provided with an adjustable counter balance and beyond fly wheel 88 the shaft is supported in bearings Il carried by a supporting bracket 84.'

Prom drum 4| the nlm strip next passes over a tensioning roller 8l and then goes to a hlm sprocket 8|, which as here shown is located above drum 4| and to one side of and somewhat lower than the rst mentioned sprocket 28. I'he film strip is retained on sprocket 8| by any conventional means, as by retaining roll 82 lmounted on pivoted arm 83. From sprocket 8| 4the film goes to sprocket 28, a slack loop being formed between the twosprockets, as indicated, and sprocket 26 feeds the lm toward the take-up reel, as previously described. As appears from Fig. 1, tensioning rollers 48 and -88 are so positioned that the nlm strip engages substantially three-quarters of the peripheral surface of drum 4|. These rollers, pressing inwardly between sprockets 28 and 8| on the one hand'and drum 4| on the other, tension the film and wrap it in driving engagement about drum 4|. As here shown, each of rollers 40 and` 88 is mounted on'a swinging arm 84 oi' a bell 'crank 88 pivoted Yat-88a, and is pressed against the iilm by a spring connected between bell crank arm 88h and a pin 81 screwthreaded within a post 88 mounted on casing wall 21. The

tension of the film strip from sprocket 28 aroundv drum 4| to sprocket 8| is adjustable by screwing adjustment pins 61 back and forth in posts 88.

Sprocket 8| is mounted on the outer end of a shaft 18 which is journalled at one end in bear- 'ings 1| supported by wall 21, and near its opposite 4eriad by'a bearing 12 carried by a plate 13 secured to the previously mentioned housing 30.

Mam drive shaft u has a gear 1t meshing with sprocket 8 I a' gear 11 formed on an annular member 18 surrounding Ashaft and relatively rotatable thereon, bearings 19 and 19a being provided between member 18 and shaft 18.

On the inner end of this member 18 there is 5 formed an .outwardly extending flange 88, and rigidly mounted on shaft 10 just rearwardly of flange 88 is an annular member 8| provided with an outwardly annular flange 82 o f the same diameter as flange 88.

Mounted on flange 82 and extending towards flange 88 are three studs 85, spaced 120 apart,l and mounted on flange 88 and extending towards flange 82 are three similar studs 86 spaced 120 apart. Studs- 85 and 86 are interconnected by 15 l tension springs 81, as indicated in Fig. 5, studs 85 and 88 thus being spaced apart normally by Y 60. Flange 80 is provided with an arcuate slot 88 which receives the projecting end of a stud 89 mounted on member 8|, the end of said stud as 20 khere shown being provided with a bushing 90.

'I'he extreme rearward end of shaft 10 is pro- I vided-with an inertia mass or fly wheel 92, which functions to. steady the rotation of shaft 10 and Main drive shaft 34 rotates gear 18 to drive gear 11 and member 18, and the rotation of member .18 is transmitted to sprocket shaft 10 through filter springs 81. The mechanical lter constituted by discs 80 and 82 and interconnecting 30 springs 81 absorbs speed irregularities or gear vibrations of the driving mechanism back of the filter, the inertia mass provided by fly wheel 92 preventing such speed irregularities from being transmitted through the. filter to shaft 18. Shaft 10 and sprocket 6| therefore rotate with a high degree of uniformity of speed.

In starting, power is transmitted through the mechanical filter by engagement of the end of arcuate slot 88 with stud 88. When the recorder 40 is up to speed, stud 8! rides at a midway position between the ends of the slot, and there is no interconnection-between discs 88 and 82 other than that afforded by springs 81.

An optical recording unit is indicated at 88, and is positioned to direct the recording light -beam against the film while supported on the face of drum 4|, said beam being of course directed to impinge on the sound track area of the film, which as previously described comes over drum surface recess 46. The optical recording unit may involve an optical system of any well known or approved type, and need not here be described in detail.

The operation of the film driving mechanism is as follows: Main drive shaft 34 is driven by a suitable driving motor, not shown. This shaft drives sprocket 20 through gears 33 and 32 and shaft 24, and also drives sprocket 6| through gears 16 and 11 and the mechanical filter con- 60 stituted' by springs 81, the shaft 18 on which sprocket 6| is mounted and which is driven from shaft 34 through said filter carrying an inertia mass in the form of fly wheel 92. Sprocket 6| is therefore driven at steady, uniform speed, speed c5 irregularities due to back lash in gears,'etc., being filtered out and prevented from transmission to said sprocket by means of the described mechanical filter and iiy wheel.

The film strip coming from the feed reel of the 70 magazine first engages one side of sprocket 20, then passes over tensioning roller 40 to engage and pass around drum 4|, and from there goes around tensioning roller to constant speed SPIOfikef 3|, after Which the film forms a slack 75 Cil loop and thenengages the opposite side of sprocket to be fed'upwardly to the take-up reel in the magazine. The nlm strip between the two sprockets is tensioned by rollers and 60, one acting between sprockets 20 and drum 4l, and the other acting between drum 4I and sprocket 6 I. This tension is made sunicientto cause drum Il to be driven by the film strip. Owing to the large inertia mass turning with this drum, the drum rotates with a high -degree of uniformity.

It will be evident that there is substantially a constant length of nlm between constant speed sprocket 6I and driven sprocket 20. Sprocket 20 serves as a driven hold-back member, while the nlm is constantly and steadily advanced by second sprocket 6l. Slight irregularities in the speed of the nlm moving toward drum 40 due to sprocket tooth action in passing over sprocket 20, or to back lash, etc., in the driving interconnections back of sprocket 20, are absorbed by yieldingly mounted tension roller 40.- Any slight irregularity in the speed ofthe nlm owing to sprocket tooth action in passing over second sprocket 6I is absorbed by yieldingly mounted tension roller r613. Thetwo yieldingly mounted tension rollers thus maintain` a constant tension in the nlm strip passing around drum Il, and at the same time serve to absorb any nnal speed irregularities owing to sprocket tooth action in passingr over the two sprockets or to the gear drive back of sprocket 20.` 'I'he inertia mass turning with drum 4| nnally assures perfectly constant speed -of 'the nlm strip passing thereover in line with the optiA same speed. The diameter of the drum is then preferably made suniciently large in relation to this nxed peripheral speed that it will turn over no more than approximately once per second, so

that the frequency of any pitch variation due to drum Aeccentri'citv will not substantially exceed one-per second, which is not considered to be objectionable for the small degree of speed variation occasioned by eccentricity lin a precision manufactured drum. It will be evident that a drum of substantially six inches in diameter or slightly less, will give the relationsdesired when 'the nlm travels at one and one half feet per second. For slower nlm speeds, used with narrow gauge nlm, the drum may of course be of correspondingly decreased diameter while still holding speed variations of the type` here being considered to a frequency of no higher than substantially one per second.v

I have now illustrated and described one preierred specinc embodiment of my invention; it is to be understood, however, that various changes in design, structure and arrangement may be made without departing from the spirit and scope of the invention or of the appended claims.

I claim:

l. Film driving means comprising two nlm drive sprockets adapted to engage spaced points ci a nlm strip, said film strip forming 'a nlm loop between said sprockets, drive, means for said .bration nlter in the driving interconnection between said drive means and the second sprocket engaged by the film strip, a nlm driven drum drivingly engaged by the nlm loop between the v two sprockets, an inertia mass rigidly associated with the second sprocket, and another inertia mass rigidly associated with the nlm driven drum. f

2. Film driving means comprising two nlm drive sprockets adapted to engage spaced points of a nlm strip, saidnlm strip forming a nlm loop between said sprockets, drive means for said sprockets, driving interconnections between said drive means and said sprockets, a mechanical vibration nlter in the driving interconnection between said drive means and the second sprocket engaged by the film, a nlm driven drum drivingly engaged by thev nlm loop between the two sprockets, yieldable nlm tensioning means for tensioning .the nlm loop between the two sprockets, an inertia mass rigidly associated with the second sprocket, and another inertia mass rigidly associated with the nlm driven drum.

3. Film driving means comprising two nlm drive sprockets adapted to engage spaced points of a nlm strip, said nlm strip forming a film loop between said sprockets, drive means for said sprockets, driving interconnections between said drive means and said sprockets, a mechanical vibration nlter in lthe driving interconnection between said drive means and the second sprocket engaged by the nlm, a film driven drum drlvingly engaged by the nlm loop between the two sprockets, an inertia mass rigidly associated with the second sprocket, another inertia mass rigidly associated with the nlm driven drum, and a yieldingly mounted tensioning roller engaging the nlm strip between the nrst sprocket and the nlm drum acting to prevent speed nuctuations of the nrst sprocket from being transmitted to the nlm drum.

4. Fihn driving means comprising two vnlm drive sprockets adapted to vengage spaced points of a nlm strip, said nlm strip forming a nlm loop between said sprockets, drive means forl said sprockets, driving interconnections between said drive means andsaid sprockets, a mechanical viy bration filter in the driving interconnection between said drive means and the second sprocket engaged by the nlm, a nlm driven drum drivingly engaged bythe nlm loop i between the two sprockets, an inertia mass rigidly associated with the second sprocket, another inertia mass rigidly associated withthe nlm driven drum, and a yieldingly mounted tensioning roller engaging the nlm strip between -the nlm drum and the second sprocket acting to prevent speed fluctuations owing to sprocket tooth action from being transmitted to said drum.

5. Film driving means comprising two nlm drive sprockets adapted toerigage spaced points of a nlm strip, said nlm strip forming a nlm loop between said sprockets, drive means for said sprockets. driving interconnections between said drive means and said sprockets, a mechanical vi-` bration nlter in the driving interconnection between said drive means and the second sprocket engaged by the nlm, a nlm driven drum drivingly engaged by the nlm loop between the two sprockets, an inertia mass rigidly associated with .mounted tensioning roller engaging thenlm strip between the nrst sprocket and the nlm drum .act-

ing -to prevent speed nuctuatlons oi' the nrst 76 sprocket from being transmitted to the nlm drum, and a yieldingly mounted tensioning roller engaging the nlm strip between the nlm drum and the second sprocket acting to prevent speed nuctuations owing to sprocket tooth action from being transmitted to said drum.

-6. Film driving means comprising two nlm drive sprockets adapted to engage spaced points of a nlm strip, said nlm strip forming a nlm loop between said sprockets, drive means for said sprockets,- driving interconnections between said drive means and said sprockets, a mechanical vibration nlter in the driving interconnection-between said drive means and the second sprocket engaged by the nlm, a comparatively large nlm driven drum drivingly engaged by. the nlm loop betweentlie two sprockets, an inertia mass rigidly associated with the second sprocket, another inertia mass rigidly associated with the nlm driven drum, a yieldingly mounted tensioning roller engaging the nlm Vstrip between the nrst sprocket and the nlm drum acting to prevent speed nuctuations of the nrst sprocket from being transmitted to the nlm drum, and a yieldingly mounted tensioning roller engaging the nlm strip between the nlm drum and the second sprocket acting to prevent speed nuctuations owing to sprocket tooth action from being transmitted to said drum.

7. Film driving means comprising two nlm drive sprockets adapted to engage spaced points of a nlm strip, said nlm strip forming a nlm loop between said sprockets, drive means for said sprockets, driving interconnections between said drive means and said sprockets, a mechanical vibration nlterjn the driving interconnection between said drive means and the second sprocket engaged by the nlm, a comparatively large nlm ldriven drum adapted to be drivingly engaged by said nlm loop, nlm guide and tensioning means for wrapping said nlm loop about substantially three quarters of the periphery of said drum, an inertia mass rigidly associated with the second sprocket, and another inertia mass rigidly associated with the nlm driven drum.

8. Film driving means comprising two nlm drive sprockets adapted to engage spaced points of a nlm strip, saidnlm strip forming a nlm loop between said sprockets, drive means for said sprockets, driving interconnections between said drive means and said sprockets, a mechanical vibration nlter in the driving interconnection between said drive means and the second sprocket engaged by the nlm, a comparatively large nlm driven drum adapted to be drivingly engaged by said nlm loop, a pair of yieldingly mounted nlm tensioning rollers located outside the nlm loop and adapted to engage the nlm loop just ahead of and just beyond the points at which it engages and leaves the drum, said nlm rollers acting to tighten the nlm loop about the nlm drum and also to'prevent speed nuctuations of the nrst sprocket and speed fluctuations owing to sprocket LoUrs B. Homann. 

